1. Technical Field
The present application relates to an electronic control apparatus having a switching element and a drive circuit, and more particularly to an electronic control apparatus used for driving motors and capable of detecting faults of the drive circuit.
2. Description of the Related Art
Conventionally, an electronic control apparatus having a switching element and a drive circuit have been employed. For example, Japanese Patent Application Laid-Open Publication No. 2007-288856 discloses a motor drive unit as an electronic control apparatus.
The motor drive unit disclosed in the above patent document includes a power transistor and a gate driver. The gate driver includes first and second current sources, a gate-current control device and a gate switching control device. The first current source is connected between the positive terminal of the power supply unit and the gate terminal of the power transistor. The second current source is connected between the gate terminal of the power transistor and the negative terminal of the power supply unit. The gate current-control device is connected to the first and second current sources. The gate switching control device is connected to the gate-current control device.
The gate current control device is adapted to drive the first power transistor by controlling the first and second current sources based on the signal inputted by the gate switching control device. In response to the signal inputted from the gate switching control device commanding the power transistor to be turned ON, the gate current control device controls the first current source to supply predetermined current into the gate. As a result, the gate voltage exceeds the threshold voltage that determines ON-OFF switching whereby the power transistor turns ON.
Meanwhile, in response to the signal inputted from the gate switching control device commanding the power transistor to be turned OFF, the gate current control device controls the second current source to sink predetermined current from the gate. As a result, the gate voltage becomes lower than the threshold voltage whereby the power transistor turns OFF.
In the above-described motor drive unit, when the first current source is in a faulty condition, the gate voltage of the power transistor does not decrease so that an abnormal condition where the power transistor cannot be turned OFF may occur. In this case, when the gate voltage of the power transistor is within a predetermined range which is close to the threshold voltage, the source-drain voltage (turn-ON voltage) of the power transistor increases so that heat produced by the power transistor increases as well. Therefore, if such an abnormal condition continues, the power transistor may be damaged by excessive heat.